This application claims priority to an application entitled xe2x80x9cData Transmission Apparatus and Method for an HARQ Data Communication Systemxe2x80x9d filed in the Korean Industrial Property Office on May 24, 2000 and assigned Ser. No. 2000-29121, the contents of which are hereby incorporated by reference.
1. Field of the Invention
The present invention relates generally to a data transmission apparatus and method in a radio communication system, and in particular, to an apparatus and method for managing retransmission of data which is subjected to transmission error during data transmission.
2. Description of the Related Art
A radio communication system chiefly uses convolutional codes, turbo codes or linear block codes, for channel coding. Such a radio communication system may employ an HARQ (Hybrid Automatic Repeat Request) Type I using an ARQ (Automatic Repeat Request) scheme which requests retransmission of data packets upon completion of decoding and CRC error check. HARQ scheme is generally applicable to a satellite system, an ISDN (Integrated Services Digital Network) system, a digital cellular system, a CDMA-2000 (Code Division Multiple Access-2000) system, a UMTS (Universal Mobile Telecommunication System) system or an IMT-2000 (International Mobile Telecommunication-2000) system, and HARQ scheme includes the convolutional codes and the turbo codes.
The above-stated hybrid ARQ scheme is generally divided into HARQ Type I, HARQ Type II and HARQ Type III. At present, most of the multi-access schemes and the multi-channel schemes using the convolutional codes or the turbo codes employ the HARQ Type I. That is, the multi-access and multi-channel schemes of the radio communication system using the above-stated channel coding scheme, employ the HARQ Type I as an ARQ scheme for increasing the data transmission efficiency, i.e., throughput of the channel coding scheme and improving the system performance.
A principle of the HARQ Type I is based on the fact that the channel encoder using the convolutional code, the turbo code or the linear block code has a constant code rate. FIGS. 1A and 1B illustrate a conceptional data process flow by the HARQ Type I.
Commonly, a transmitter of the radio communication system combines L-bits transmission data with a CRC (Cyclic Redundancy Check) code for error detection and then encodes the combined data, L+CRC, through channel coding. The transmitter transmits the encoded data through an assigned channel. Meanwhile, a receiver of the radio communication system acquires the original L-bits data and the CRC code through a reverse operation of the transmitter, and transmits a response signal ACK/NAK to the transmitter according to the CRC check results.
This will be described in more detail with reference to FIG. 1A. A CRC encoder 110 receives an L-bits source data packet and encodes the received data using a CRC code, creating a FEC input data block, L+CRC. Commonly, CRC bits are added to the source data before channel encoding. A channel encoder 112 performs channel coding on the FEC input data block, L+CRC, creating a channel-coded data block, (L+CRC)xc3x97Rxe2x88x921. The channel-coded data block, (L+CRC)xc3x97Rxe2x88x921, is provided to a specific channel through other functional blocks 114 necessary for multiplexing.
Other inverse functional blocks 124 necessary for demultiplexing in the receiver receiving the channel-coded data block through the specific channel, demultiplex the received coded data block and output a channel-coded data block, (L+CRC)xc3x97Rxe2x88x921. A channel decoder 122 then performs channel decoding on the channel-coded data block, (L+CRC)xc3x97Rxe2x88x921, and outputs a channel-decoded data block, L+CRC. A CRC decoder 120 performs CRC decoding on the channel-decoded data block, L+CRC, to acquire the original data, i.e., the L-bits source data packet. After completion of CRC decoding, the CRC decoder 120 performs CRC checking using the CRC decoding results, thereby to determine whether the source data packet has transmission errors.
If no error is detected through the CRC check, the receiver provides the source data packet to an upper layer and transmits a confirm signal ACK (Acknowledgement) acknowledging the source data packet to the transmitter. However, upon detecting an error through the CRC check, the receiver transmits a confirm signal NAK (Not-Acknowledgement) requesting retransmission of the channel coded data packet to the transmitter.
After transmitting the channel-coded data block, the transmitter receives the confirm signal ACK/NAK from the receiver in response to the transmitted channel-coded data block. Upon receipt of the confirm signal NAK, the transmitter retransmits the corresponding channel-coded data block in the above-described operation. The transmission scheme includes Stop-and-Wait ARQ, Go-Back-N ARQ, and Selective-Repeat ARQ schemes. The detailed description of the retransmission schemes will be omitted.
FIG. 1B illustrates a conceptual transmission procedure of the channel-coded data packet between the transmitter and the receiver. FIG. 1B shows that the transmitter retransmits the channel-coded data block upon every receipt of m NAKs from the receiver.
As an example of such a procedure, in an air interface of the 3GPP-2 (3rd Generation Partnership Project-2; a standard for a synchronous CDMA system) mobile communication system (hereinafter, referred to as xe2x80x9cCDMA-2000xe2x80x9d system), the multi-access scheme and the multi-channel scheme of the system employ the HARQ Type I in order to increase data transmission efficiency of the channel coding scheme and to improve the system performance. In addition, in an air interface of the 3GPP (3rd Generation Partnership Project; a standard for an asynchronous CDMA system) mobile communication system (hereinafter, referred to as xe2x80x9cUMTS systemxe2x80x9d), the multi-access scheme and the multi-channel scheme of the system also employ the HARQ Type I in order to increase data transmission efficiency of the channel coding scheme and to improve the system performance.
However, the HARQ Type I has the following disadvantages.
First, the HARQ Type I has higher throughput, compared with a pure ARQ scheme. However, as a signal-to-noise ratio (S/N) of a signal is increased more and more, the throughput becomes saturated to a code rate R of the FEC code, thus resulting in a reduction in the throughput as compared with the pure ARQ. That is, the throughput cannot approach 1.0 (100%) even at very high S/N. Such a problem is shown by a characteristic curve of the HARQ Type I in FIG. 2. That is, as for the HARQ Type I, the throughput is saturated to the code rate R ( less than 1.0) as shown in FIG. 2, so that it cannot approach 1.0.
Second, the HARQ Type I improves the throughput by performing error correction using the FEC code, compared with the pure ARQ. However, since the HARQ Type I uses a constant redundancy, i.e., constant code rate regardless of variation in S/N, it has low transmission efficiency. Therefore, the HARQ Type I cannot adaptively cope with variations in the channel condition, thus causing limitation of throughput.
To solve such problems, the HARQ Type II or the HARQ Type III is used. The HARQ Type II and the HARQ Type III have an adaptive structure which adaptively determines an amount of redundancies used for the FEC code according to how good the channel condition is. Therefore, the HARQ Type II and the HARQ Type III have improved throughput, compared with the HARQ Type I. That is, the adaptive structure reduces the amount of redundancies to a minimum, so that as the S/N of the signal is increased more and more, the code rate R of the FEC code approaches 1, thereby enabling the throughput to approach 1. Meanwhile, the adaptive structure performs optimal error correction such that if the S/N of the signal is decreased, the amount of redundancies is increased to a maximum to enable the code rate R of the FEC code to approach 0, or the redundancies are repeated so as not to enable the throughput to approach 0. Accordingly, the HARQ Type II and the HARQ Type III have improved throughput at both a low S/N and a high S/N.
The HARQ Type I, the HARQ Type II and the HARQ Type III transmit the response signal ACK/NAK, channel condition indication bit, or packet number through a control channel or a through control message channel in response to the received channel-coded data block. In the following description, the channel for transmitting the response signal or control signal message will be referred to as xe2x80x9cmessage channelxe2x80x9d, and the message transmitted over the message channel will be referred to as xe2x80x9ccontrol message.xe2x80x9d
The message channel can be divided into a forward message channel and a reverse message channel according to the transmitting subject. The HARQ Type I, the HARQ Type II and the HARQ Type III generally use a reverse message channel as a response channel. On the other hand, sort of response message, ACK/NACK, can be transmitted on physical control channel. The reverse message channel is used when the receiver transmits to the transmitter the signal indicating the receiving results of the received data block.
In some cases, however, the HARQ Type I uses the forward message channel according to the ARQ scheme. For example, when using a Selective Repeat ARQ (SR-ARQ) scheme, the HARQ Type I transmits a serial number of every data block transmitted from the transmitter to the receiver over the forward message channel. Meanwhile, the HARQ Type II and the HARQ Type III transmit a redundancy version used during each retransmission in addition to the serial number of the data block generated during each redundancy retransmission to the receiver through the forward message channel.
One of the important factors for guaranteeing performance of the HARQ Type I, the HARQ Type II and the HARQ Type III is reliability of a message channel transmitting the control message.
For example, upon failure to correctly receive the response signal ACK transmitted from the receiver in response to the transmitted data block due to an error of the reverse message channel, the transmitter will continuously retransmit the erroneous data block even though the receiver didn""t request retransmission of the data block. Such a problem takes place even in the forward message channel as well as the reverse message channel. That is, upon failure to correctly receive the control message, for example, the data block""s serial number and the redundancy type transmitted from the transmitter due to an error of the forward message channel, the receiver will endeavor to decode the erroneous data block retransmitted from the transmitter.
Therefore, in order to solve the above problem, the HARQ scheme is required to use a message channel having higher reliability compared with the channel transmitting the data block. In addition, a response speed of the message channel, i.e., how fast the message channel can transmit the message, is also an important factor in determining performance of the HARQ scheme.
However, to date there has not been proposed a concrete design rule for one case where the multi-access scheme and the multi-channel scheme of the 3GPP-2 CDMA-2000 system including the existing data communication system employ the channel coding scheme (HARQ Type I), and another case where the multi-access scheme and the multi-channel scheme of the 3GPP UMTS system employ the HARQ Type II and the HARQ Type III. That is, since a transmission method and scheme of the message channel in the HARQ Type II and the HARQ Type III used by the existing data systems has been not duly considered, there may occur a performance-related problem. Therefore, in order to optimize performance of the HARQ scheme, it is necessary to realize an HARQ Type II/III message channel satisfying the foregoing description.
In addition, to date there has not been proposed a concrete method for transmitting the message channel for one case where the multi-access scheme and the multi-channel scheme of the CDMA-2000 system including the conventional data communication system employ the channel coding scheme (HARQ Type I), and another case where the multi-access scheme and the multi-channel scheme of the UMTS system employ the HARQ Type II and the HARQ Type III, or a modified HARQ Type I using symbol combining.
It is, therefore, an object of the present invention to provide an apparatus and method for increasing reliability of a message channel in an HARQ data communication system.
It is another object of the present invention to provide an apparatus and method for increasing reliability of a message channel by assigning bit redundancy of a data block transport channel as a message channel.
It is a further object of the present invention to provide a transmission scheme designed considering the conditions necessary for a message channel most efficient in an HARQ Type II and an HARQ Type III or a modified HARQ Type I using symbol combining.
It is yet another object of the present invention to provide a message channel for a high-speed HARQ scheme, structured to increase its response speed.
It is still another object of the present invention to provide an apparatus and method for transmitting a control message over a message channel in an HARQ data communication system using convolutional codes.
It is still another object of the present invention to provide an apparatus and method for transmitting a control message over a message channel in an HARQ data communication system using turbo codes.
It is still another object of the present invention to provide an apparatus and method for transmitting a control message over a message channel in an HARQ data communication system using linear block codes.
It is still another object of the present invention to provide an apparatus and method for transmitting a control message over a message channel in an HARQ data communication system using convolutional codes, turbo codes and linear block codes.
It is still another object of the present invention to provide an apparatus and method for transmitting a control message over a message channel in a most efficient manner in an HARQ scheme of an asynchronous mobile communication system.
To achieve the above and other objects, there is provided an apparatus provided with a plurality of transport channels, for transmitting a data block having a sequence of data bits and a control message having control bits required in decoding the sequence of data bits. A first rate matching part provided in a selected one of the transport channels, passing the data block, punctures a predetermined number of data bits from the data bits within the data block. A second rate matching part provided in another transport channel, repeats the control bits for as many as the predetermined number of punctured bits.
Preferably, the second transport channel includes the control message arranged at either the head or tail thereof.
Preferably, the control message includes a serial number of a transmission data block, a version number of a given data block and a redundancy type in a given version.
Preferably, the second transport channel has a transmission delay time equal to or less than that of the first transport channel.